3. It has been found that young animals, birds, etc., depend upon the example and instruction of adults for the first performance of many actions that seem to be instinctive. This dependence may exist even in cases in which there is yet a congenital tendency to perform the action. Many birds, for example, have a general instinct to build a nest; but in many cases, if put in artificial circumstances, they build imperfect nests. Birds also have an instinct to make vocal calls; but if kept from birth out of hearing of the peculiar notes of their species, they come to make cries of a different sort, or learn to make the notes of some other species with which they are thrown. 4. The principal agency for the learning of the animals, and for the supplementing of their instincts, is Imitation. The sight of certain movements on the part of the adult animals, or the hearing of their cries, calls, notes, etc., leads the young to fall into an imitation of these movements or vocal performances. The endowment which such a young animal has in the direction of making movements and cries similar to those of his species aids him, of course, in imitating these in preference to others. So the endowment and the tendency to imitate directly aid each other in all such functions, and hurry the little creature on in his acquisition of the habits of his species. We find young animals clinging even in their imitations pretty closely to their own proper fathers and mothers, who are thus enabled to bring them up _comme il faut_. 5. There is every reason to think, moreover, that the tendency to imitate is itself instinctive. Young animals, notably the monkey and the child, fall spontaneously to imitating when they reach a certain age. Imitation shows itself to be instinctive in the case of the mocking bird, the parrot, etc. Furthermore, the mechanism of this function of imitation is now very well known. The principle of psychology recognised above under the phrase Kinaesthetic Equivalents, teaches us that the idea of a movement, coming into the mind through sight or some other sense, stirs up the proper apparatus to bring about the same movement in the observer. This we see in the common tendency of an audience to repeat the gestures of a speaker, and in many similar cases. When this principle is extended to include all sorts of experiences besides those of movement, we have what is generally called Imitation. Moreover, every time that by action the child imitates, he perceives his own imitation, and this again acts as a "copy" or model for another repetition of the act, and so on. This method of keeping himself going gives the young animal or child constant practice, and renders him more and more efficient in the acts necessary to his life.